A wildfire in the Crazy Mountains in Helena-Lewis and Clark National Forest south of Two Dot has ballooned from 500 to an estimated 4,000 to 5,000 acres.

The Blacktail Fire was reported on Sunday in the Blacktail Creek area, east of Loco Mountain in the Crazy Mountains in Meagher County.

Lightning caused it.

"We did have some campers and recreationists in the area that were evacuated, but we haven't evacuated any primary or secondary residences," said Erin Fryer, public information officer assigned to the fire.

The evacuation, which involved about 10 people, was a precautionary measure, Fryer said.

Tuesday afternoon, the fire burned out of the forest and onto private ranch lands, she said.

No structures were lost.

Smokejumpers and a helicopter are assigned to work on the fire, which is actively burning in steep and rugged terrain.

Volunteers firefighters from Two Dot, Melville and Sweet Grass County were a big part in the early firefighting efforts, Fryer said.

Because of winds, the fire grew significantly Tuesday, said Kathy Bushnell, a spokeswoman with Helena-Lewis and Clark National Forest.

The Blacktail fire is burning in the Crazy Mountains south of Two Dot in Meagher County.(Photo: InciWeb)

The most active part of the fire moved east and private landowners in that general were notified, but no pre-evacuations had been issued, Bushnell said.

Winds were strong Wednesday. The way the terrain is situated in the area, it funnels the wind, Fryer said.

Numerous snags and dead/down fuel is a challenge for firefighters, who are working where it is safe to do so, the Forest Service said.